1. Field of the Invention
Embodiments of the present invention generally relate to a method of improving microelectronic device lifetime. In particular, embodiments of the present invention generally relate to improving electromigration lifetime of copper interconnection structures.
2. Description of the Related Art
Microelectronic devices, such as semiconductors or integrated circuits (IC), can include millions of electronic circuit devices such as transistors, capacitors, etc., such as found in ultra-large scale integrated (ULSI) circuits. To further increase the density of devices found on integrated circuits, smaller and smaller feature sizes are necessary. For example, the size of conductive lines, vias, and interconnects, gates, etc. must decrease. Reliable formation of multilevel interconnection structures of ULSI technology is also necessary to increase circuit density and quality. Advances in IC fabrication techniques have enabled use of copper conductive lines, interconnects, vias, and other structures. However, with decreased feature size and the increased use of copper interconnect structures, electromigration in interconnect structures becomes a greater hurdle to overcome.
Hundreds, if not thousands of processing steps are required to form an IC. Usually the steps will include deposition, etching, rapid thermal processing (RTP), oxidation, film growth, ion implantation, chemical-mechanical polishing (CMP), photolithography, etc. to form various features in the microelectronic device. As a final processing step, sometimes the substrate is annealed at a temperature of about 350° C. to 400° C. for a time duration between about 30 minutes to about 1 hour. When forming interconnect structures by means of such processing steps, electromigration remains a large hurdle to overcome.
Electromigration is the transport of material caused by the gradual movement of the atoms in a conductor due to the momentum transfer between conducting electrons and diffusing metal atoms that can cause depletion or accumulation of metal atoms. During normal, regular use of microelectronic devices, electrons collide with metal atoms causing the atoms to gradually move. This movement may cause a depletion of atoms at the negative end of the conductor, leading to voids, thinning of lines, and a potential open circuit.
In other regions of the conductor, an accumulation of metal atoms may pile up and form hillocks, protrusions on the surface of metal films due to electromigration. If excessive or large hillocks form, adjacent lines or lines on two levels may short together.
Increased current density and chip temperature, attendant with the advanced circuitry designs in the ULSI technology, make the metallization or interconnect structure more prone to electromigration. Thus, methods of further improving electromigration in interconnect structures of microelectronic devices are needed.